Chimney stacks take more punishment than almost any other part of a roof. They stand proud of the roofline, exposed to weather from every direction. The brickwork and pointing holding them together eventually give way. That’s why chimney work is one of the most consistent call-outs we get across Putney’s period housing.
Why chimneys fail before the rest of the roof
A chimney stack sits well above the surrounding roof. It takes the full force of wind-driven rain from every angle. The main roof slope, by contrast, sheds most of the weather in one direction. So that exposure accelerates wear on the mortar joints between the bricks. As a result, repointing that would last decades on a sheltered wall can fail much sooner on an exposed stack. A working flue also heats and cools the brickwork around it. That thermal movement is why chimneys are often the first thing to need attention on an otherwise sound roof.
Repointing: the most common chimney repair
Repointing means raking out the old, failed mortar between the bricks. We replace it with new mortar, mixed to match the original as closely as possible. On period properties, this matters more than it sounds. That’s because a modern cement-heavy mix is harder and less porous than the traditional lime mortar many Victorian and Edwardian chimneys were built with. As a result, using the wrong mix can trap moisture in the brick and speed up frost damage rather than prevent it. So we match mortar to the age and construction of the stack, not whatever’s quickest to buy.
Flaunching: the chimney’s cap
Flaunching is the sloped mortar cap at the top of the stack. It holds the pots in place and sheds rainwater away from the flue openings. Because of its position, it’s exposed to more extreme weathering than almost any other part of the roof. So cracked or crumbling flaunching is one of the most common chimney problems we find, particularly on stacks that haven’t been inspected in years. Left unrepaired, water gets in around the pots and tracks down inside the flue and stack — a slower route for water ingress than a leak through the roof, but just as damaging.
Flashing: where the chimney meets the roof
The lead flashing dressed around the base of a chimney stack is one of the most failure-prone details on the whole building. We cover this in more depth in our guide to lead flashing and leadwork. The chimney moves slightly independently of the roof around it, so this joint works loose over time, even when it was installed correctly. A chimney leak is very often a flashing problem, not a problem with the stack’s brickwork at all. That’s why we check both before diagnosing the cause.
When a stack needs a full rebuild
Repointing and flaunching repairs address surface-level wear. But a stack with badly spalled or crumbling bricks, or one leaning visibly out of true, has gone beyond what repointing alone can fix. In these cases, a partial or full rebuild is the safer, longer-term repair — taking the stack down to sound brickwork and rebuilding upward, given the stack’s height and exposure to wind loading.
What we check on every chimney inspection
On every chimney inspection across Putney, Chelsea and Wandsworth, we look at the pointing, the flaunching, the flashing at the base, and the general condition of the brickwork before recommending a fix. Most chimney problems are caught well before a rebuild becomes necessary, provided they’re picked up early. That’s the main argument for having a stack looked at periodically, rather than waiting for a leak to appear.
Noticed cracked pointing, crumbling flaunching, or a chimney-related leak? Get in touch for a free inspection of your chimney and an honest recommendation on what it needs.